Textbook Ch.6: Electronic Structure and the Periodic Table
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Wavelength (λ)
the distance between two consecutive crests or troughs, most often measured in meters or nanometres 1nm = 10⁻⁹ m
Frequency (v)
the number of wave cycles (successive crests or troughs) that pass a given point in unit time.
Hertz (Hz)
the frequency unit that represents one cycle per second v = 10⁸m/s = 10⁸ Hz
Speed of light in a vacuum (c)
2.998*10⁸ m/s
How can you find the speed at which a wave moves through space?
λv = c • λ should be expressed in meters • v should be expressed in reciprocal seconds (hertz)
Photons
a stream of particles that we consider light and has the energy E
What equation gives the energy of photons?
E.= hv = hc/λ
Joule (J)
an SI unit for energy
Kilojoules
1kJ = 10³ J
Planck’s equation / Planck’s constant
h = 6.62610⁻³⁴ Js
Energy is ____ related to wavelength
inversely
Bohr’s atomic model
assumed that a hydrogen atom consists of a central proton about which an electron moves in a circular orbit
Bohr’s equation for the energy of the hydrogen electron:
E = -R / n^2 E = energy of the electron R = Rydberg constant (2.180 * 10⁻¹⁸ J) n = principal quantum number (depends on the state of the electron)
Rydberg constant
2.180 * 10⁻¹⁸ J
In Bohr’s model, where did he designate the zero energy point?
the point at which the proton and electron are completely separated • Energy has to be absorbed to reach that point • The electron must have an energy below zero
Ground state / ground level
the hydrogen electron being in its lowest energy state n=1
Excited state
when the hydrogen electron absorbs enough energy and moves to a higher state 1st excited state: n = 2 2nd excited state: n = 3 and so on…
When will an electron drop back to a lower energy state?
when if gives off energy as a photon of light • It can return to ground state (from n=2 to n=1) • It can go to a lower excited state (from n=3 to n=2)
The energy of the photon (hv) evolved is equal to:
the difference in energy between the two states ∆E = hv = Eₕᵢ - Eₗₒ
What equations can be used to relate the frequency of light emitted to the quantum numbers nₕᵢ and nₗₒ of the two states:
hv = -Rₕ - ( 1/(nₕᵢ)² - 1/(nₗₒ)² ) v = Rₕ / h( 1/(nₕᵢ)² - 1/(nₗₒ)² )
Quantum mechanics
the science dealing with the behavior of matter and light on the atomic and subatomic scale
How does the quantum mechanical atom differ from the Bohr model?
• The kinetic energy of an electron is inversely related to the volume of the region to which it is confined • It is impossible to specify the precise position of an electron in an atom at a given instant
𝚿
• the symbol for wave function • for the hydrogen electron, 𝚿² is directly proportional to the probability of finding the electron at a particular point
Electron cloud diagram
shows how 𝚿² for the hydrogen in its ground state (n=1) varies moving out from the nucleus